Catalyst to attain low sulfur gasoline

ABSTRACT

This invention relates to a hydrodesulfurization catalyst, a method for preparing the catalyst, and a method for the preparation of low sulfur gasoline fuel with minimal loss of RON. The catalyst particles include a group VIB metal and a support material having relatively high surface area, and optionally includes one or more group VIIIB metal. The method for preparing the catalyst allows for greater loading of the active metal species on the surface of the support material under aqueous reaction conditions.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 14/595,601, filed on Jan. 13, 2015, which is a divisionalapplication of U.S. patent application Ser. No. 12/390,706, filed onFeb. 23, 2009, and now U.S. Pat. No. 9,636,662, which claims priority toU.S. Provisional Patent Application Ser. No. 61/030,352, filed on Feb.21, 2008, each of which are incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Technical Field of the Invention

This invention generally relates to the field of hydroprocessingcatalysts for treatment of hydrocarbons. In particular, the presentinvention is directed to a process for preparing a catalyst useful forthe hydrodesulfurization of gasoline feedstock with minimal loss ofoctane rating.

Description of the Prior Art

In the petroleum industry, it is common for gas oils, particularlymiddle distillate petroleum fuels, to contain sulfur species. Enginesutilizing petroleum based fuels that include sulfur produce emissions ofnitrogen oxide, sulfur oxide and particulate matter. Governmentregulations have become more stringent in recent years with respect toallowable levels of the potentially harmful emissions.

Many countries around the world currently limit allowable sulfur contentin gasoline fuels to less than 50 ppm, and in some cases as low as 20ppm. As environmental concerns grow, allowable sulfur content ingasoline fuels may soon be limited to 10 ppm or less. Thus, catalystsand processes for the production of gasoline fuels having a sulfurcontent of 10 ppm or less are needed.

Various methods have been proposed to reduce sulfur levels in gas oils.However, there are disadvantages associated with previously proposedmethods. For example, hydrodesulfurization of fuel in catalytic reactorshas been proposed, however the process frequently requires two or morereactors operating in series under severe reaction contidions; i.e., lowflow rates and high temperatures, pressures and hydrogen consumptionconditions. The severe reaction conditions are necessary to overcomestrong inhibition by refractory sulfur and nitrogen compounds againsthydrodesulfurization. Therefore, strict conditions are also imposed onapparatus design, thereby typically incurring high construction costs.

Alternatively, various organic and inorganic adsorbents have beenproposed to effectuate adsorptive removal of sulfur compounds. Examplesof previously proposed adsorbents include silica, alumina, zeolite,activated carbon, activated carbon-based fiber materials and spenthydrodesulfurization catalyst. However, the volumetric adsorptioncapacity for these adsorbents was often too low, and breakthrough ofsulfur compounds into the fuel product was often too rapid. Also,inorganic adsorbents typically require high temperature treatment forregeneration, which is not practical for stable and continuousoperation, and the adsorption regeneration cycle can be too frequent,which makes efficient operation difficult. Further, these adsorbentsoften can be expensive and susceptible to attrition. Fine particlesproduced due to attrition between adsorbent particles can cause pluggingand high pressure drop, each of which can shorten the run length of anadsorption process.

Catalytic desulfurization is one method for removal of sulfur ofhydrocarbons. Generally, catalytic desulfurization takes place atelevated temperature and pressure in the presence of hydrogen. At theelevated temperatures and pressures, catalytic desulfurization canresult in the hydrogenation of other compounds, such as for example,olefin compounds, which may be present in the petroleum fraction whichis being desulfurized. Hydrogenation of olefin products is undesirableas the olefins play an important role providing higher octane ratings(RON) of the feedstock. Thus, unintentional hydrogenation of olefincompounds during desulfurizationmay result in a decreased overall octanerating for the feedstock. If there is significant loss of octane ratingduring the hydrodesulfurization of the hydrocarbon stream, because ofsaturation of olefin compounds, the octane loss must be compensated forby blending substantial amounts of reformate, isomerate and alkylateinto the gasoline fuel. The blending of additional compounds to increasethe octane rating is typically expensive and thus detrimental to theoverall economy of the refining process.

Additionally, catalytic hydrodesulfurization can result in the formationof hydrogen sulfide as a byproduct. Hydrogen sulfide produced in thismanner can recombine with species present in the hydrocarbon feed, andcreate additional or other sulfur containing species. Olefins are oneexemplary species prone to recombination with hydrogen sulfide togenerate organic sulfides and thiols. This reformation to produceorganic sulfides and thiols can limit the total attainable sulfurcontent which may be achieved by conventional catalytic desulfurization.

Alumina is a common support material used for catalyst compositions, buthas several disadvantages in the desulfurization of petroleumdistillates. Alumina, which is acidic, may not be well suited for thepreparation of desulfurization catalysts with high loading of activecatalytic species (i.e., greater than 10 weight %) for catalyticallycracked gasoline. Acidic sites present on the alumina support facilitatethe saturation of olefins, which in turn results in the loss of octanerating of gasoline. Additionally, recombination of the olefin withhydrogen sulfide, an inevitable result of hydrodesulfurization, producesorganic sulfur compounds. Furthermore, basic species present in thefeedstock, such as many nitrogen containing compounds, can bind toacidic sites on the surface of the alumina and the catalyst, therebylimiting the number of surface sites which are available for sulfurcompounds for desulfurization. Furthermore, basic species present in thefeedstock, such as many nitrogen containing compounds, can bind toacidic sites on the surface of the alumina and the catalyst, therebylimiting the number of surface sites which are available for sulfurcompounds for desulfurization. At the same time, nitrogen containingcompounds having aromatic rings are easily transformed into cokeprecursors, resulting in rapid coking of the catalyst. Additionally,high dispersion of the metal is difficult to enhance with an aluminasupport due to the strong polarity and the limited surface area of thealumina. Exemplary commercially available hydrotreating catalystsemploying an alumina support include, but are not limited to,CoMo/Al₂O₃, NiMo/Al₂O₃, CoMoP/Al₂O₃, NiMoP/Al₂O₃, CoMoB/Al₂O₃,NiMoB/Al₂O₃, CoMoPB/Al₂O₃, NiMoPB/Al₂O₃, NiCoMo/Al₂O₃, NiCoMoP/Al₂O₃,NiCoMOB/Al₂O₃, and NiCoMoPB/Al₂O₃, (wherein Co is the element cobalt, Niis nickel, Mo is molybdenum, P is phosphorous, B is boron, Al isaluminum and O is oxygen).

In addition, prior art methods suffer in that the preparation ofdesulfurization catalysts having high metal loading with high dispersionis generally difficult. For example, many prior art catalysts areprepared by a conventional impregnation method wherein the catalysts areprepared by mixing the support materials with a solution that includesmetal compounds, followed by filtration, drying, calcination andactivation. However, catalyst particles prepared by this method aregenerally limited in the amount of metal which can be loaded to thesupport material with high dispersion, which generally does not exceedapproximately 25% by weight of the metal oxide to the support material.Attempts to achieve higher loading of the metal to support materialshaving a relatively high surface area, such as silicon dioxide,typically result in the formation of aggregates of metallic compounds onthe surface of the support. Activated carbon has much higher surfacearea and weaker polarity than conventional catalyst supports, such asfor example, alumina and silica. This provides improved performance inthe desulfurization of catalytically cracked gasoline because botholefin saturation and recombination of hydrogen sulfide with the olefinare suppressed over activated carbon support. However, weaker polarityand a relatively high hydrophobicity make activated carbon difficult toload large amount of active metallic species, such as molybdenum oxide.

Thus, catalyst compositions and methods for preparing catalysts usefulfor the removal of sulfur species from petroleum based products areneeded. Specifically, methods for the production of the catalystcompositions which include support materials having high surface areaand high catalyst loading with high dispersion for the desulfurizationof petroleum products are desired.

SUMMARY OF THE INVENTION

A hydrodesulfuriztion catalyst composition, a method for the preparationof the catalyst composition and a method for preparing low sulfurgasoline fuel from catalytically cracked gasoline are provided. Thecatalyst particles include at least one active metal and a supportmaterial.

In one aspect, a method for preparing a hydrodesulfurization catalyst isprovided. The method includes the steps of preparing a mixture thatincludes at least one metal salt, a catalyst support and water, whereinthe metal salt is selected from a salt of molybdenum, chromium andtungsten. The mixture is prepared under vacuum. The mixture can also beprepared in an inert atmosphere. Water is removed from the mixture andthe catalyst particles are collected. The particles are calcined byheating the particles to a temperature of greater than about 200° C. Thecalcined catalyst particles are then partially sulfided by contactingthe catalyst particles with a gas stream having up to about 5% by volumehydrogen sulfide in the presence of hydrogen.

In certain embodiments, the mixture can include a second metal saltwherein the metal is selected from the group consisting of iron,ruthenium, osmium, cobalt, rhenium, iridium, nickel, palladium andplatinum. The molar ratio of the first metal to the second metal isbetween about 1.5:1 and 5:1. In certain embodiments, the mixture caninclude a molybdenum metal salt and a second metal salt selected from acobalt metal salt and a nickel metal salt. In certain embodiments, thesurface area of the catalyst support material is greater than about 500m²/g. In certain embodiments, the oxide form of the first metal ispresent in an amount of between about 10% and 30% by weight of thecatalyst support material.

In another aspect, a method of preparing a desulfurization catalyst isprovided. The method includes the steps of preparing a first mixturethat includes a molybdenum salt, a catalyst support and water, whereinthe first mixture is under vacuum. The water is removed from the firstmixture to produce a catalyst precursor. A second mixture is preparedthat includes a metal salt selected from a nickel or cobalt salt, waterand the catalyst precursor, which was prepared from the first mixture.Water is removed from the second mixture to produce catalyst particles.The catalyst particles are calcinated by heating the particles to atemperature of greater than about 200° C. and the calcinated catalystparticles are partially sulfided by contacting the catalyst particleswith a gas stream comprising up to about 5% by volume hydrogen sulfide.

In another aspect, a catalyst composition is provided. The catalystcomposition includes an activated carbon catalyst support material, afirst metal selected from the group consisting of chromium, molybdenumand tungsten, and a second metal selected from the group consisting ofiron, ruthenium, osmium, cobalt, rhenium, iridium, nickel, palladium andplatinum. The first metal is present in its oxide form in an amount ofbetween 10 and 30 weight % of the support material and the second metalis present in an amount of between about 1 and 10% by weight of thesupport material. Both the first and second metals are present in theoxide form of the metal.

In another aspect, a method for the hydrodesulfurizing a petroleum basedhydrocarbon distillate is provided. The method includes contacting apetroleum hydrocarbon distillate with hydrogen gas in the presence of ahydrodesulfurization catalyst, wherein the hydrodesulfurization catalystcomprises an activated carbon catalyst support material, a first metalselected from the group consisting of chromium, molybdenum and tungsten,a second metal selected from the group consisting of iron, ruthenium,osmium, cobalt, rhenium, iridium, nickel, palladium and platinum, andthe hydrodesulfurization catalyst that includes between about 10 and 30%by weight of the first metal and between about 1 and 10% by weight ofthe second metal.

DETAILED DESCRIPTION OF THE INVENTION

Gasoline hydrodesulfurization catalysts preferably have highhydrodesulfurization activity and low hydrogenation activity of olefins.Conventional methods for the preparation of nickel-molybdenum (NiMo) orcobalt-molybdenum (CoMo) catalysts supported on activated carbon canresult in catalysts having less than about 5% by weight MoO₃, andnon-uniform aggregates of the metal oxide. The drawbacks associated withthe conventional methods for preparing catalysts on activated carbonlimit the catalytic performance in the desulfurization of hydrocarbons,and particular in the desulfurization of catalytically cracked gasoline.Preferably, the metal oxide forms a thin uniform layer on the surface ofthe support material. Additionally, it is preferred that the metal ispresent in an amount greater than approximately 15% by weight of thesupport material to enhance catalytic conversion of sulfur compounds.

Catalyst

The catalyst includes a support material and at least one active metal.

The catalyst support can be selected from activated carbon, activatedcarbon fiber, carbon black, activated carbon fabric, activated carbonhoneycomb, metal oxides including silicon dioxide, titanium dioxide,zirconium dioxide, and the like, and combinations thereof. Activatedcarbon and carbon black are believed enhance the activity of the metalspecies due to relatively weak polarity and relatively high surfacearea. In certain embodiments, the surface area of the support materialcan be at least about 200 m²/g. In other embodiments, the surface areacan be at least about 300 m²/g. In preferred embodiments, the surfacearea can be at least about 500 m²/g, more preferably at least about 1000m²/g. In certain embodiments, the pore diameter can be between about 0.5nm and 5 nm. In certain other embodiments, the pore diameter can bebetween about 1.5 nm and 4 nm.

The catalyst composition can at least one active metal selected fromGroup VIB of the periodic table, which includes, chromium, molybdenumand tungsten. The catalyst can also include at least one promoter metalselected from the Group VIIIB metals of the periodic table, whichinclude iron, ruthenium, osmium, cobalt, rhenium, iridium, nickel,palladium and platinum, as the active component. In certain embodiments,the catalyst composition can include more than one Group VIIIB metal. Ina preferred embodiment, the catalyst can include molybdenum. In certainother preferred embodiments the catalyst composition can include eithercobalt or nickel. Optionally, at least a portion of the metal can bepresent as a metal sulfide. Alternatively, at least a portion of themetal can be present as a metal oxide.

The group VIB metal can be present in oxide form and can be loaded ontothe support material in an amount exceeding approximately 10% by weightof the support material. In other embodiments, the group VIB metal oxidecan be loaded onto the support material in an amount exceedingapproximately 15% by weight of the support material. In yet otherembodiments, the group VIB metal oxide can be loaded onto the supportmaterial in an amount exceeding approximately 20% by weight of thesupport material. In yet other embodiments, the group VIB metal oxidecan be loaded onto the support material in an amount exceedingapproximately 25% by weight of the support material. In certainpreferred embodiments, the metal oxide can be MoO₃.

The group VIIIB metal can be present in oxide form and can be loadedonto the support in an amount exceeding approximately 1% by weight ofthe support material. In other embodiments, the group VIIIB metal oxidecan be present in an amount between about 1% and 10% by weight of thesupport material. In other embodiments, the group VIIIB metal oxide canbe present in an amount between about 4% and 10% by weight of thesupport material.

Known catalyst promoters can also be added to the catalyst composition.Exemplary catalyst promoters can include, but are not limited to, boronand phosphorous.

The catalyst composition can be subjected to calcining or similarthermal treatment, which can be beneficial by increasing the thermalstability and metal dispersion of the catalyst composition. Generally,during calcination, the particles are heated in an oxygen containingenvironment to temperatures ranging from about 200° C.-800° C. Theprocess can be carried out by placing the composition in a processheater, at the desired temperature, with a flowing oxygen containinggas, such as for example, atmospheric air. The process heater can beheated to the designated temperature or temperature range, maintained atthe designated temperature for a defined time period, and then cooled toroom temperature. The calcination of the catalyst composition caninclude heating the catalyst particles at a defined ramp rate.

Prior to use, the catalyst can be exposed to a sulfur source for thepreparation of surface bound metal sulfides. The sulfur source can becontacted with the catalyst in either liquid or gaseous form. In certainembodiments, the catalyst particles can be contacted with a hydrogen gasmixture that includes hydrogen sulfide. In one exemplary embodiment, thesulfur source is a hydrogen gas stream that can include up toapproximately 10% hydrogen sulfide by volume. Alternatively, thehydrogen gas stream includes between approximately 1 and 5% hydrogensulfide by volume. In certain embodiments, the catalyst particles can becontacted with a sulfur source at a temperature of greater than about200° C., preferably at temperatures greater than about 300° C.

Catalyst Preparation

In another aspect, a method for preparing a hydrodesulfurizationcatalyst composition from an aqueous solution is provided. Generally,activated carbon species are hydrophobic. Thus, preparation of catalystsusing activated carbon supports generally requires the use of organicsolvents to reduce hydrophobicity of the carbon support surface, or toenhance the affinity of the metal species to the surface of theactivated carbon. Methods of preparing catalysts employing carbonsupports from aqueous solutions generally result in low catalystloading. A catalytic support material can be placed under vacuum tofacilitate the removal of trapped solvent and/or moisture. In certainembodiments, the catalytic support material can be heated under vacuum.Exemplary conditions for the catalyst preparation include heating thecatalytic support material to a temperature of up to about 100° C. andapplying vacuum up to a pressure of approximately 1 torr or less.Without being bound to any specific theory, it is believed that treatingthe catalytic support material under vacuum can facilitate diffusion ofthe metal species into the small pores.

A mixture can be prepared by adding a metal salt solution that includesat least one metal salt and water, to the support under vacuum. Themetal salt solution can be added to the catalyst support materialslowly. Optionally, in certain embodiments, it may be advantageous thatthe metal salt solution is added dropwise to the catalyst supportmaterial.

Exemplary catalytic support materials can include, but are not limitedto, activated carbon, activated carbon fiber, carbon black, activatedcarbon fabric, activated carbon honeycomb, metal oxides includingsilicon dioxide, titanium dioxide, zirconium dioxide, and the like, andcombinations thereof. In a preferred embodiment, the catalyst supportmaterial is an activated carbon species.

In certain preferred embodiments, the catalyst support material can beneutral or basic, when compared to the gamma-type alumina, which isfrequently used as the support material for desulfurization catalysts.For use in the desulfurization of hydrocarbon streams, in particularcatalytically cracked gasoline, which can typically include olefins andproduce hydrogen sulfide as a product of the hydrodesulfurization, thecatalyst support material is preferably not acidic. Without wishing tobe bound by any theory, it is believed that acidic sites on a supportmaterial can facilitate olefin saturation, which can result in RON loss,and recombination of hydrogen sulfide with olefin, which limitattainable sulfur content of product. Any RON loss must then becompensated for by the addition of expensive alkylates, isomeratesand/or other chemicals.

Catalyst support materials having a high surface area allow for greaterloading of the active species which provide the catalytic activity.Thus, catalyst support materials having a relatively high surface areaare preferred. In other embodiments, the catalyst support materialsurface area can be at least about 200 m²/g. In certain embodiments, thecatalyst support material surface area is at least about 300 m²/g.Preferably, the catalyst support material surface area is at least about500 m²/g. Even more preferably, the catalyst support material has asurface area of at least about 1000 m²/g.

The catalyst support material particles can have a diameter of betweenabout 0.5 and 10 mm, preferably between about 1 and 8 mm in diameter,and even more preferably approximately 5 mm in diameter. In certainother embodiments, the catalyst support material particles can have apore diameter of less than about 15 nm. In yet other embodiments, thecatalyst support material particles can have a pore diameter of lessthan about 10 nm.

Exemplary catalyst support materials having low acidity and high surfacearea include activated carbon species. Activated carbons are exemplarycatalyst support materials that can be advantageously used to preparehydrodesulfurization catalysts, according to the methods describedherein.

Exemplary metal salts can include salts of the Group VIB metals of theperiodic table, which include chromium, molybdenum and tungsten. Incertain embodiments, exemplary metal salts can include salts of theVIIIB metals, which include iron, ruthenium, osmium, cobalt, rhenium,iridium, nickel, palladium and platinum. In certain embodiments, themetal salt includes a metal that is preferably selected from cobalt,molybdenum and nickel. In other embodiments, more than one metal saltcan be added to the solution, wherein at least one of the metals isselected from cobalt, molybdenum and nickel. Preferably, the metalsalt(s) and catalyst support material are sufficiently mixed to producea homogeneous aqueous solution that contains the metal salt and thesupport material. Specific examples of metal salts which can be employedaccording to the methods disclosed herein include, but are not limitedto, (NH₄)₆Mo₇O₂₄.4H₂O, Ni(NO₃)₂.6H₂O, Co(NO₃)₂.6H₂O, NiCl₂.6H₂O,CoCl₂.6H₂O, (NH₄)₆H₂W₁₂O₄₀.XH₂O (ammonium metatungstate), and the like.Nickel and cobalt acetates can also be used as precursors, although, forpurposes of solubility, organic solvents may be required. Optionally,finely ground particles of molybdenum trioxide can also be used toprepare a colloidal precursor solution.

The mixture can be mechanically mixed to ensure adequate interactionbetween the catalyst support material and the metal salts. Mixing can beaccomplished by known means, such as for example, by ultrasonicvibration, by mechanical stirring means, or other means known in theart. In certain embodiments, a mixture that includes water, catalystsupport material and the metal salt can be mixed for at least about 15minutes. In other embodiments, the mixture can be mixed for a period ofat least about 1 hour. In yet other embodiments, the mixture can bemixed for a period of between about 4 and 6 hours.

After mixing, the mixing vessel can be exposed to atmospheric conditionsand the water can be removed. Optionally, the mixture can be heated toassist in the evolution of water and gases. In certain otherembodiments, the solids can be collected by filtration. In certainpreferred embodiments, the mixture can be first heated, followed byremoval of the remained of the liquids under vacuum. In otherembodiments, the mixture is heated to a temperature of between about 40°C. and 150° C., preferably between about 60° C. and 130° C. In certainembodiments, the mixture is heated to a temperature of greater thanabout 100° C. In certain other embodiments, the mixture is heated to atemperature of approximately 120° C. In certain embodiments, the mixtureis stirred while the catalyst is heated. In certain embodiments, liquidscan be removed under a vacuum of up to about 1 torr. In certainpreferred embodiments, remaining liquids can be removed under a vacuumof approximately 1 torr, for a period of approximately 16 hours.

The particles can be calcinated after collection and drying at atemperature of between about 200° C. to 600° C. In certain embodiments,the catalyst particles are calcinated at a temperature between about200° C. and 500° C. In preferred embodiments, the catalyst particles arecalcinated at a temperature of between about 250° C. and 350° C.Optionally, the catalyst particles can be calcinated at a temperature ofapproximately 300° C. The catalyst particles can be calcinated forbetween about 30 minutes and 8 hours, preferably for between 3-6 hours.In an exemplary embodiment, the catalyst particles are calcinated at atemperature of approximately 320° C. for a period of approximately 3hours. Optionally, calcination can be done in an oxygen containingenvironment, preferably in air. Without being bound to any theory,calcination in air is believed to form the oxidic precursor form of themetal as the active phase of the catalyst.

After being dried and collected, the catalyst particles can be contactedwith a sulfur containing source. The sulfur containing source can be agas or liquid source. In certain embodiments, the catalyst particles canbe contacted with a hydrogen gas mixture that includes hydrogen sulfide.Optionally, the sulfur source is a hydrogen gas stream which can includeup to approximately 10% hydrogen sulfide by volume. Alternatively, thehydrogen gas stream includes between approximately 1 and 5% hydrogensulfide by volume. In certain embodiments, the catalyst particles can becontacted with a sulfur source at a temperature of greater than about100° C., preferably at temperatures greater than about 200° C., and mostpreferably at a temperature greater than about 300° C. In an exemplaryembodiment, the catalyst particles can be contacted with a sulfurcontaining source at a temperature of approximately 360° C. Preferably,the sulfur containing hydrogen gas can contact the catalyst particlesfor an extended period of time, such as for example, at least one hour,or more preferably, at least two hours. The effluent leaving thecatalyst during pre-sulfiding has sulfur content lower than that of theeffluent being fed, thus showing active sulfidation of the oxidic formof the catalyst particles.

Catalytic Desulfurization

In one aspect, a method of producing a reduced sulfur gasoline isprovided.

The method includes the steps of contacting a gasoline feedstockprepared by the catalytic cracking gasoline with a desulfurizationcatalyst wherein the desulfurization catalyst includes an activatedcarbon support having one or more of a Group VIB and a Group VIIIB metalsulfide adsorbed on the surface.

The hydrocarbon feedstock can be a derivative from crude petroleum oil,oil sands, oil shale, or oil derived from coal or wood. Generally, anyhydrocarbon oil that includes sulfur or sulfur impurities, can be usedas a suitable hydrocarbon feedstock. Typically, modern gasoline is ablend of several different refinery streams, including reformate,straight run naphtha, catalytically cracked gasoline, coker naphtha,isomerate, alkylate and oxygenate. The main source of sulfur contenttypically comes from FCC gasoline, coker naphtha and straight runnaphtha obtained from high sulfur crudes.

Desulfurization can take place in a reactor, such as for example, afixed bed, packed bed, slurry bed or fluidized bed reactor, which can becharged with an activated carbon supported desulfurization catalyst,which can be prepared as described herein. Typically, the gasolinefeedstock, hydrogen gas and the catalyst are contacted in a reactor,typically at an elevated temperature. The desulfurization can take placeat a temperature of at least about 200° C. In certain embodiments, thedesulfurization takes place at a temperature of between about 250° C.and 400° C. Typically pressures can be between about 100 and 500 psig.The LHSV can be between about 2 and 10 h⁻¹, preferably betweenapproximately 4 and 8 h⁻¹. The ratio of hydrogen gas to feedstock can befrom about 20-200 L/L, preferably from about 50-150 L/L, more preferablyapproximately 110-130 L/L.

The overall process can include multiple reactors arranged in parallel.This arrangement allows for continuous operation of the desulfurizationprocess while allowing for the simultaneous regeneration of spentcatalyst.

The process and catalyst described herein are advantageously solidheterogeneous catalysts. Because the catalyst is a heterogeneouscatalyst, there is no need to determine suitable organic solvents forsolubility of the catalyst and hydrocarbonaceous feedstock.Additionally, because the catalyst is a solid material, and dissolutionof catalyst in reaction matrix is not an important aspect of thedesulfurization, there is never any need to separately remove solvent ordissolved catalyst from the effluent.

EXAMPLES

Example 1 provides a method for the preparation of an exemplaryhydrodesulfurization catalyst that includes molybdenum and cobalt on anactivated carbon support. An HCN (heavy cat naphtha) fraction distilledfrom a FRCN (full range cat naphtha) is treated with thehydrodesulfurization catalyst prepared according to the proceduredescribed in Example 1. Example 2 describes the hydrodesulfurization ofan HCN fraction distilled from a FRCN with a commercially availabledesulfurization catalyst. The results are compared in Table 6.

Example 1

A 20.0 g sample of dried and purified activated carbon (Norit) havingspecific surface area of 1,065 m²/g and average pore diameter of 2.2 nmwas placed in a 200 mL flask. The flask was then evacuated under vacuumfor approximately 16 hours to a pressure of approximately 1 torr. Anaqueous solution was prepared by dissolving 4.91 g (0.00397 mol) of(NH₄)₆Mo₇O₂₄.4H₂O (Fluka) to make 20 mL (0.20 M) aqueous solution. Theaqueous solution (20 mL) was added dropwise and shaken over a period ofabout 5 minutes into the flask, which was maintained under vacuum, andmixed for approximately 6 hours. Following mixing, the flask was ventedto the atmosphere and heated at a temperature of approximately 120° C.until the atmospheric vaporization of water ceased. The flask was cooledto room temperature and evacuated under vacuum to a pressure ofapproximately 1 torr for approximately 16 hours.

An 8.02 g (0.00649 mol) sample of (NH₄)₆Mo₇O₂₄.4H₂O (Fluka) wasdissolved in water to make 40 mL (0.16 M) aqueous solution. A 20 mLsample of the aqueous solution was introduced to the flask dropwise overabout a 5 minute period with shaking, under vacuum, and mixed forapproximately 6 hours. The flask was vented to atmosphere and to atemperature of approximately 70° C. until the atmospheric vaporizationof water ceased. The flask was cooled to room temperature and evacuatedunder vacuum to a pressure of approximately 1 torr for approximately 16hours again.

A 7.06 g (0.0243 mol) sample of Co(NO₃)₂.6H₂O (Aldrich Chem.) wasdissolved in water to make a 20 mL aqueous solution (1.2 M). The aqueoussolution (20 mL) was introduced to the flask dropwise over about a 5minute period with shaking, under vacuum, and mixed for approximately 6hours. After mixing, the flask was vented to atmosphere and heated to atemperature of approximately 70° C. until the atmospheric vaporizationof water ceased. The contents of the flask, a black powder, wastransferred to an alumina crucible, heated at a rate of approximately 2°C./min to about 320° C. and calcinated for approximately 3 hours underatmosphere. The catalyst product (29 g) was collected as a blackparticulate material, consisting of approximately 25 wt % molybdenumoxide and 6.2 wt % cobalt oxide.

A full range cat naphtha (FRCN) feedstock was distilled to produce aheavy cat naphtha (HCN) stream. Properties of feedstocks are outlined inTable 1.

TABLE 1 FRCN HCN A Total Sulfur (ppm) 2467 665 Total Nitrogen (ppm) 19 6Composition, wt % (ASTM-D5134) Aromatics 22.2 36.2 I-Paraffins 27.3 26.9Napthenes 14.2 17.1 n-Olefins 10.7 6.1 I-Olefins 12.0 4.6 Cyclic-Olefins1.5 0.5 Total Olefins 23.5 13.4 Paraffins 5.5 4.3 Unidentified 4.0 2.1Distillation (ASTM-D2887) (° C.)  5% 39 91 10% 46 99 20% 57 112 40% 85127 50% 103 141 70% 143 153 90% 191 173

The HCN A catalyst described in Table 1 above was hydrotreated withapproximately 10 mL of the catalyst, prepared as described above, whichwas pre-sulfided at 320° C. for 12 hours with straight run naphthaspiked with dimethyldisulfide to have a sulfur content of approximately2.5 wt %. Operating conditions for hydrotreatment of HCN are summarizedin Table 2.

TABLE 2 Run 29 Run 30 Run 31 Pressure (psig) 300.0 300 300 Temperature(° C.) 280 300 341 LHSV (h⁻¹) 6.1 5.8 6.0 H₂/Oil (L/L) 119 119 119

The liquid products from Runs 29, 30 and 31 were analyzed as shown inTable 3.

TABLE 3 Liquid Liquid Liquid Product Product Product from Run 29 fromRun 30 from Run 31 Total Sulfur (ppm) 90 30 7 Total Nitrogen (ppm) 1.71.5 1.7 RON Loss 4.5 5.2 9.7 Distillation (ASTM D2887)  5% 91 87 84 10%96 98 92 20% 105 112 104 40% 123 128 120 50% 132 138 129 70% 150 156 14890% 171 172 169

Example 2

The HCN A described in Table 1 above was hydrotreated with approximately10 mL of a commercially available Cobalt/Molybdenum hydrotreatingcatalyst having an alumina support and a surface area of approximately250 m²/g. The catalyst was pre-sulfided at 320° C. for approximately 12hours with straight run naphtha spiked with dimethyldisulfide to have2.5 wt % sulfur. The operating conditions for hydrotreatment of the HCNfraction are summarized in Table 4.

TABLE 4 Run 4 Run 5 Run 6 Pressure (psig) 300 300 300 Temperature (° C.)260 300 330 LHSV (h⁻¹) 6.1 6.1 6.0 H₂/Oil (L/L) 118 118 118

Liquid products from Run 4, 5 and Run 6 were analyzed as shown in Table5.

TABLE 5 Liquid Product Liquid Product Liquid Product from Run 4 from Run5 from Run 6 Total Sulfur (ppm) 571 216 55 Total Nitrogen (ppm) 2.4 1.41.3 RON Loss 0.6 1.7 5.8 Distillation (ASTM D2887) (° C.)  5% 89 89 8710% 96 97 94 20% 105 108 104 40% 122 126 120 50% 130 136 129 70% 148 153147 90% 169 172 168

The results are presented in comparative form below, wherein thehydrodesulfurization temperatures, resulting sulfur content and percent(%) conversion for the desulfurization of HCN using a the catalystprepared according to Example 1 (corresponding to Tables 2 and 3, Runs29, 30 and 31) and the commercially available hydrotreating catalystprepared according to Example 2 (corresponding to Tables 4 and 5, Runs4, 5 and 6).

TABLE 6 Hydrotreatment with Catalyst Prepared Hydrotreatment withCommercially According to Example 1 Available Catalyst Accordin toExample 2 Temp. (° C.) Sulfur (ppm) % Conversion Temp. (° C.) Sulfur(ppm) % Conversion 280 90 86.5 260 571 14.2 300 30 95.4 300 216 67.5 3417 98.9 330 55 91.7

As shown in the above tables and summarized in Table 6, hydrotreatmentof HCN with the catalyst prepared according to the methods described inExample 1 resulted in a HCN product stream having much lower sulfurcontents than the product stream from hydrotreatment with a commerciallyavailable alumina supported catalyst. Hydrotreatment at a temperature of300° C. with the catalyst of Example 1 achieved an HCN product streamhaving approximately 30 ppm sulfur while similar hydrotreatment with thecommercially available alumina supported catalyst of Example 2 producedan HCN product stream having approximately 216 ppm sulfur. Thoseparticular sulfur contents correspond to sulfur conversions ofapproximately 95.4% and 67.5%, respectively. Desufurization with thecommercially available alumina supported catalyst of Example 2 resultedin a sulfur conversion of approximately 91.9% 340° C. In contrast, ultradeep sulfur conversion was achieved with the catalyst prepared accordingto Example 1 during hydrotreatment at a temperature of approximately341° C., wherein the process resulted in a sulfur conversion ofapproximately 98.9%, and produced a product stream having a sulfurcontent of approximately 7 ppm.

Loss of RON, estimated by PIONA data, was less for desulfurization withthe catalyst of Example 1 than with the commercially available aluminasupported catalyst of Example 2 for relatively similar conversion rates.For example, the catalyst of Example 1 had an RON loss of approximately5.2 at 97.5% sulfur conversion (Run 30, 300° C.) and an RON loss ofapproximately 9.7 at 98.9% sulfur conversion (Run 31, 341° C.). Incontrast, the commercially catalyst of Example 2 had an RON loss ofapproximately 5.8 at 91.9% sulfur conversion (Run 6, 330° C.). Thus, itis shown that the catalyst prepared according to Example 1 can achievehigher conversion (95.4% desulfurization vs. 91.7% desulfurization), atless severe conditions (300° C. vs. 330° C.), and a lower loss of RON(5.2 vs. 5.8). In addition, it is shown that the catalyst preparedaccording to Example 1 can achieve much higher sulfur conversion thanthe commercially available catalyst of Example 2 under severe reactionconditions (98.9% conversion corresponding to a sulfur content of 7 ppmat a desulfurization temperature of 341° C. vs. 91.7% conversioncorresponding to a sulfur content of 55 ppm at 330° C.).

As used herein, the terms about and approximately should be interpretedto include any values which are within 5% of the recited value.Furthermore, recitation of the term about and approximately with respectto a range of values should be interpreted to include both the upper andlower end of the recited range.

While the invention has been shown or described in only some of itsembodiments, it should be apparent to those skilled in the art that itis not so limited, but is susceptible to various changes withoutdeparting from the scope of the invention.

We claim:
 1. A method for hydrodesulfurizing a petroleum basedhydrocarbon distillate comprising: contacting the petroleum hydrocarbondistillate with hydrogen gas in the presence of a hydrodesulfurizationcatalyst, wherein the petroleum hydrocarbon distillate includes sulfuror sulfur impurities; wherein the hydrodesulfurization catalyst consistsof an activated carbon catalyst support material, a first metal in oxideform and selected from the group consisting of chromium, molybdenum andtungsten, and a second metal in oxide form and selected from the groupconsisting of iron, ruthenium, osmium, cobalt, rhenium, iridium, nickel,palladium and platinum, the activated carbon catalyst support materialconsisting of a basic or neutral activated carbon; wherein thehydrodesulfurization catalyst consists of between about 15 and 30% byweight of the oxide form of the first metal and between about 1 and 10%by weight of the oxide form of the second metal, wherein the molar ratioof the first metal to the second metal is between 1.5:1 and 5:1.
 2. Themethod of claim 1 wherein the hydrodesulfurization catalyst is preparedby the process comprising: preparing a mixture comprising at least onemetal salt, a catalyst support and water, wherein the mixture is undervacuum; removing the water from the mixture and collecting the catalystparticles; calcinating the particles by heating the particles to atemperature of greater than about 200° C.; and partially sulfiding thecatalyst particles by contacting the calcined catalyst particles with agas stream comprising up to about 5% by volume hydrogen sulfide; whereinthe metal salt comprises a first metal selected from the groupconsisting of chromium, molybdenum, and tungsten.
 3. The method of claim1 wherein the hydrodesulfurization catalyst consists of about 20% byweight molybdenum and at least about 2% by weight nickel.
 4. The methodof claim 1 wherein the hydrodesulfurization catalyst consists of about20% by weight molybdenum and at least about 2% by weight cobalt.
 5. Themethod of claim 1, wherein the petroleum hydrocarbon distillatecomprises fluid catalytic cracking (FCC) gasoline, coker naphtha andstraight run naphtha.